About Creating Django-treebeard Hierarchies in Data Migrations
Django-treebeard API is not accessible in Django migrations, therefore, you would need to use low-level concepts to create a hierarchical tree in a data migration.
When you use Materialized Paths for the hierarchical models, the model could look like this:
# categories/models.py
from django.db import models
from treebeard.mp_tree import MP_Node
class Category(MP_Node):
title = models.CharField("Title", max_length=255)
class Meta:
verbose_name = "Category"
verbose_name_plural = "Categories"
def __str__(self):
return self.title
And the migration creating a category tree on the fly could look like this:
# categories/migrations/0002_create_categories.py
from django.db import migrations
def create_categories(apps, schema_editor):
from treebeard.numconv import NumConv
alphabet = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"
number_converter = NumConv(radix=len(alphabet), alphabet=alphabet)
category_tree = [
{
"title": "Fruits",
"children": [
{"title": "Apples"},
{"title": "Bananas"},
],
},
{
"title": "Vegetables",
"children": [
{"title": "Potatoes"},
{"title": "Carrots"},
],
},
]
Category = apps.get_model("categories", "Category")
for root_index, root_category_dict in enumerate(category_tree, 1):
root = Category.objects.create(
path=f"{number_converter.int2str(root_index):0>4}",
depth=1,
numchild=0,
title=root_category_dict["title"],
)
for leaf_index, leaf_category_dict in enumerate(
root_category_dict["children"], 1
):
leaf = Category.objects.create(
path=(
f"{number_converter.int2str(root_index):0>4}"
f"{number_converter.int2str(leaf_index):0>4}"
),
depth=2,
numchild=0,
title=leaf_category_dict["title"],
)
root.numchild += 1
root.save(update_fields=["numchild"])
def dummy(apps, schema_editor):
pass
class Migration(migrations.Migration):
dependencies = [
("categories", "0001_initial"),
]
operations = [
migrations.RunPython(create_categories, dummy),
]
Here the paths for the categories will be like:
0001
00010001
00010002
...
0002
...
0009
000A
000B
...
Tips and Tricks Programming Databases Django 5.x Django 4.2 Django 3.2 Python 3 django-treebeard
Also by me
Django Paddle Subscriptions app
For Django-based SaaS projects.
Django GDPR Cookie Consent app
For Django websites that use cookies.
